September 19, 2011
Yawning For Brain Temperature Regulation?

People yawn less when the outdoor temperature exceeds body temperature.

A study led by Andrew Gallup, a postdoctoral research associate in Princeton University's Department of Ecology and Evolutionary Biology, is the first involving humans to show that yawning frequency varies with the season and that people are less likely to yawn when the heat outdoors exceeds body temperature. Gallup and his co-author Omar Eldakar, a postdoctoral fellow in the University of Arizona's Center for Insect Science, report this month in the journal Frontiers in Evolutionary Neuroscience that this seasonal disparity indicates that yawning could serve as a method for regulating brain temperature.

Years ago I read the speculation that yawning's purpose was to show one's teeth to scare away predators. That didn't seem plausible. This theory seems more plausible. Though why would yawning happen more when tired?

The body can't do yawn air heat exchange to cool the brain if the air temperature is too high.

Gallup and Eldakar documented the yawning frequency of 160 people in the winter and summer in Tucson, Ariz., with 80 people for each season. They found that participants were more likely to yawn in the winter, as opposed to the summer when ambient temperatures were equal to or exceeding body temperature. The researchers concluded that warmer temperatures provide no relief for overheated brains, which, according to the thermoregulatory theory of yawning, stay cool via a heat exchange with the air drawn in during a yawn.

Does the brain get hotter when it is fatigued? I am currently reading Roy Baumeister and John Tierney's excellent book Willpower and wonder whether conditions that deplete willpower also heat up the brain.

Share |      Randall Parker, 2011 September 19 10:46 PM  Brain Innate

PacRim Jim said at September 20, 2011 12:09 AM:

Last time I heard, it was to regulate the CO2 level.

SarcastiCarrie said at September 21, 2011 9:20 AM:

I'll go with people are more tired in the winter due to lower sunlight levels, so they yawn more (to increase oxygen levels and perk them up).

The False God said at September 22, 2011 11:20 AM:

Makes more sense to regulate the CO2 level in the blood stream, which would explain why it happens so often in crowded rooms with poor ventillation.

Now, explain why it's contagious.

Chad said at September 22, 2011 11:22 AM:

I'm going to agree with SarcastiCarrie. If they want to be convincing about temperatures they needed to control for altitude and daylight. The change in ambient daylight between summer and winter are too large a variable to overlook.

Greg F said at September 22, 2011 11:30 AM:

How about the fact that in the winter you have to expend more energy to maintain your body temperature. Even when inside during the winter the humidity is likely lower than in the summer making evaporative cooling more efficient.

Koblog said at September 22, 2011 12:39 PM:

Can I get a couple grant$ to do a silly, inconclusive "study" linking human yawning, evolution and insects?

edh said at September 22, 2011 1:16 PM:

I thought yawning was about blood flow to the head (brain), which I assume would indirectly affect brain temp.

Colder external temp => Yawn => increase blood circulation to the head => warm the brain?

jocon307 said at September 22, 2011 2:17 PM:

I ALWAYS yawn when I'm cold. I also yawn when I'm sleepy. I've always been very aware that I'm yawning because I'm cold, but other people I've asked about this seem to think I'm a weirdo.

CavernousYawn said at September 22, 2011 2:32 PM:

Seems likely it's not that the brain gets hotter when it's fatigued, but that you feel sleepy when your brain is too hot, which might be a result of fatigue via some other mechanism. And jocon307, I yawn when cold too. Then there's the psychological-based yawns, like when you face something really unpleasant in the near future; I don't know what that might have to do with brain temps.

egoist said at September 22, 2011 3:42 PM:

On the flip side, I recently learned that an ice-cream headrush is really triggered by your corroded arteries (along your throat) delivering cold blood to the top of your head. It's not via the roof of your mouth. I never yawn when I do that.

Doug Jones said at September 22, 2011 3:54 PM:

Social "science" researchers are total fucking morons. They didn't test the SAME people in summer and winter, just an utterly uncontrolled random grab of passersby. Garbage in, garbage out.

Doug Jones said at September 22, 2011 3:56 PM:

Correction: *these* social science researchers are morons. The others have not been examined in sufficient detail to draw a conclusion. [grin]

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